1. Technical Field of the Invention
The present invention relates to a scanning device for reading an image, and more particularly, to a scanning device which adopts a reverse scanning control method wherein a scanner for reading an image is arranged to move to a farthest end portion of an original document in a forward moving action, and to scan the original document in a reverse moving action.
2. Description of Related Art
As a method for detecting a size of an original document placed on a predetermined position of an original document table, Japanese Published Unexamined Patent Application No.186923/1989 discloses a method for conducting a preliminary scanning operation for detecting a size of the original document before performing a regular scanning operation for reading an image of the original document.
In the case when a size of the original document is detected by conducting a preliminary scanning operation prior to a regular scanning of the original document in such a way as described above, information on the original document can be accurately grasped preliminarily. However, such two scanning operations conducted for one image reading process results in a loss in speed of copying.
In order to solve the problem, a Japanese official gazette TOKUHYO HEI 2-503738 discloses a scanning apparatus which adopts the above-mentioned reverse scanning control method. In the apparatus, an original scanning means is arranged to detect a size of an original document in a forward direction scan wherein said means is moved to a farthest end portion of the original document, and in a reverse direction scan, an image of the original document is read so that one scanning operation satisfies one image reading process, thereby increasing speed of the copying operation.
In recent years, an electrophotographic copying machine which is provided with an original document feed apparatus for automatically feeding an original document to a predetermined position on an original document table has been used widely in order to increase copying speed when a large quantity of original documents are copied. Such an apparatus is also applied to an image reading device for collecting and processing a large quantity of original documents.
In a device which is provided with said document feed apparatus, it is arranged to detect a size of an original document being transported by the original document feed apparatus. It is, therefore, not necessary to adopt the preliminary scanning method or the reverse scanning method mentioned above when the original document is automatically fed to a predetermined position on an original document table provided in a main body of the image reading device. If such scanning methods are indiscriminately adopted even when the original document feed apparatus is used, a scanning operation has to be wastefully performed in the case of the preliminary scanning method, and in the case of the reverse scanning control method, a time to start an image reading operation is meaninglessly delayed since a reverse action for a reverse scanning is performed for an original document which has been automatically fed.
It may be considered to adopt a reverse scanning control method in the case when an original document is manually set on a predetermined position of an original document table without using the original feed apparatus since the original document is specific in size and form such as a book which is not adaptable to the original feed apparatus or when original documents to be copied are small in number. The ordinary scanning method can be alternating adopted when original documents are fed automatically by the original feed apparatus.
However, there still remains a problem that it necessitates a process to temporarily store an image information which has been read in order to decide whether the original document feed apparatus is required or not which eventually causes an increase in manufacturing cost, and there occurs defect in soft control. Moreover, a construction of the device becomes complicated since it is necessary to move a scanner in reciprocating motion for reading an image of an original document in forward and reverse directions, and high accuracy is required to provide a proper tension to a driving wire for the reciprocating motion to further increase manufacturing cost.